The present invention relates to a vibration control apparatus and method used when the vibration of a movable element influences the control accuracy in a field where high-speed, high-accuracy position/speed control is required for a semiconductor exposure apparatus, machine tool, OA device, and the like.
A prior art will be described by exemplifying stage control of a semiconductor exposure apparatus.
As the exposure line width has decreased in a semiconductor exposure apparatus, the position control accuracy required for the wafer stage of the exposure apparatus has reached several nm order. For higher productivity, the stage moving acceleration and speed are increasing year by year. To realize high-speed, high-accuracy position control, the wafer stage position control system must have a high servo band. A high servo band exhibits a high response characteristic to a target value, realizing a system resistant to the influence of disturbance or the like. In manufacturing an apparatus, the wafer stage and main body structure are so designed as to realize a servo band as high as possible.
FIG. 10 is a view showing the schematic arrangement of the wafer stage of a conventional semiconductor exposure apparatus. In the following description, three translation axes (X, Y, and Z) of standard coordinates and three rotation axes (xcex8x, xcex8y, and xcex8z) around the three translation axes will be called a position with six degrees of freedom. The arrangement and operation of a high-speed, high-accuracy position control system will be explained using this example.
Reference numeral 41 denotes a surface plate which is supported via a damper from a floor F; and 43, a Y stage which can be moved in the Y direction on the reference plane of the surface plate 41 by Y linear motors 46 for generating a thrust in the Y direction along a guide 42 fixed to the surface plate 41. The surface plate 41, fixed guide 42, and Y stage 43 are coupled in a noncontact manner by air via air pads 44a and 44b serving as hydrostatic bearings. The Y stage 43 has an X guide, which guides an X stage 45 mounted on the Y stage in the X direction. The Y stage 43 has an X linear motor stator which generates a force in the X direction. The X linear motor stator drives the X stage 45 in the X direction together with an X linear motor movable element mounted on the X stage. The surface plate 41, X guide, and X stage 45 are coupled in a noncontact manner by air via an air pad 44c serving as a hydrostatic bearing.
The X stage 45 supports a tilt stage 48. The tilt stage 48 moves in the Z direction and rotates along the three axes (xcex8x, xcex8y, and xcex8z) by a thrust from a linear motor (not shown). The tilt stage 48 supports a stage plate 51 having a wafer chuck, which holds a wafer 53 to be exposed. Measurement mirrors 49a and 49b used to measure X and Y positions are arranged on the stage plate 51.
The stage device of the semiconductor exposure apparatus is aligned with six degrees of freedom in in-plane directions (X, Y, and xcex8z) and vertical directions (Z, xcex8x, and xcex8y) with respect to the reference plane of the surface plate, and performs exposure of one chip. Positions in the in-plane directions (X, Y, and xcex8z) are measured using a laser interferometer 50 integrated with a lens barrel (not shown). As for measurement in the tilt directions (Z, xcex8x, and xcex8y), a Z position and the angle of a rotational component are measured by an alignment measurement system (not shown) integrated with the lens barrel.
In FIG. 10, the lens barrel is assumed to be integrated with the surface plate, and the laser interferometer 50 is connected to the surface plate. Although no Z measurement device is illustrated, the tilt directions (Z, xcex8x, and xcex8y) can be measured by measuring three points on the stage plate or wafer from the lens barrel.
Alignment along the six axes is achieved by arranging a servo system for each axis. A compensation device calculates driving command values to the X and Y linear motors serving as X and Y stage actuators on the basis of position information of the laser interferometer, driving the X and Y stages. The compensation device calculates a driving command value to the tilt stage in accordance with the Z position, the angles in the rotational directions (xcex8x and xcex8y), and the xcex8z measurement value, driving the tilt stage.
The position control system having this arrangement can move the wafer stage to a target position at a high speed and high accuracy.
The resolution of the exposure line width is high in the stage device of the semiconductor exposure apparatus, and the position control accuracy must be high. Also, the semiconductor exposure apparatus, which is a production equipment, must have high throughput in terms of productivity. To meet these demands, the stage servo system must have a high response characteristic and move at a high speed. To increase the stage position control accuracy, the designer realizes a high servo band by setting the gain of the position control system as high as possible. However, if the designer tries to set the gain higher, its upper limit is restricted by the oscillation of the servo system. The servo band is restricted by various factors, one of which is the elastic vibration of a mechanical system in the control loop.
FIG. 8 shows the analysis result of the elastic vibration mode of the wafer stage plate 51. The primary to quaternary elastic vibration modes are illustrated. Such a thin plate is low in Z rigidity and vibrates by elastic deformation such as bending or twist. The transfer characteristic from the Z actuator to a measurement point at this time is shown in FIG. 9, and the resonance point of elastic vibration has a high peak. If, for example, the loop gain of the Z position control system is increased in this system, the resonance point of elastic vibration is excited, decreasing the stage control accuracy. With a loop gain low to a given degree, merely a large vibration appears. With a higher gain, the servo system becomes unstable and oscillates.
In this fashion, the stage plate (top plate) and the like generate elastic vibrations, and the servo system becomes unstable. Even if the servo system does not become unstable, the control error increases, failing to satisfy control specifications. In general, the servo band is restricted to about ⅓ to xc2xc the lowest resonance frequency of the elastic vibration.
In the conventional position control system, the servo band of the position control system is restricted by the resonance frequency of the elastic vibration of an object to be controlled. To realize a higher servo band, the resonance frequency of the elastic vibration must be increased, or the damping characteristic must be enhanced. For this purpose, the rigidity of an object to be controlled is increased, its mass is decreased, or the damping characteristic of the elastic vibration is enhanced. However, mechanical measures such as a decrease in stage mass, an increase in rigidity, and enhancement of the damping characteristic are limited, and it is difficult to increase the servo band.
The present invention has been made to overcome the conventional drawbacks, and has as its object to constitute a high-accuracy position control system even for a low-rigidity object to be controlled.
To solve the above-described problem and achieve the above object, according to the first aspect of the present invention, a vibration control apparatus is characterized by comprising a measurement device which measures an elastic vibration of an object to be controlled, a driving device which applies a force to the object, and a compensation device which determines a force to be generated by the driving device, wherein the measurement device measures at least a position component out of the position component, a speed component, and an acceleration component of the elastic vibration, and the compensation device controls the elastic vibration of the object on the basis of position information measured by the measurement device.
The vibration control apparatus according to the present invention is characterized in that the object to be controlled is supported by a spring in a noncontact manner.
The vibration control apparatus according to the present invention is characterized in that a higher vibration mode can be controlled by connecting, to the object to be controlled, pluralities of driving devices and measurement devices.
The vibration control apparatus according to the present invention is characterized in that an in-plane vibration of the elastic vibration is controlled by arranging at least one of the plurality of driving devices so as to prevent a force acting direction from being parallel.
The vibration control apparatus according to the present invention is characterized in that at least two of the plurality of driving devices are so arranged as to make force acting directions substantially perpendicular to each other.
The vibration control apparatus according to the present invention is characterized in that the object to be controlled includes a stage top plate of an exposure apparatus, the measurement device includes a piezoelectric element attached to the top plate, and the driving device includes a piezoelectric element attached to the top plate.
A vibration control apparatus according to the present invention is characterized by comprising a first measurement device which measures an elastic vibration of an object to be controlled, a first driving device which applies a force to the object, a first compensation device which determines a force to be generated by the driving device, a second measurement device which measures a position of the object from a reference position, a second driving device which externally applies a force to the object, and a second compensation device which determines a force to be generated by the second driving device, wherein the first measurement device measures at least a speed component out of a position component, the speed component, and an acceleration component of the elastic vibration, the first compensation device controls the elastic vibration of the object on the basis of speed information measured by the first measurement device, and the second compensation device controls a rigid-body vibration of the object on the basis of position information measured by the second measurement device.
According to the second aspect of the present invention, an exposure apparatus is characterized by using the above-described vibration control apparatus for a stage.
According to the third aspect of the present invention, a device manufacturing method is characterized by comprising the steps of applying a photosensitive material to a substrate, transferring a pattern to the photosensitive material on the substrate coated with the photosensitive material by the above-described exposure apparatus, and developing the substrate bearing the pattern.
According to the fourth aspect of the present invention, a vibration control method using a vibration control apparatus having a measurement device which measures an elastic vibration of an object to be controlled, a driving device which applies a force to the object, and a compensation device which determines a force to be generated by the driving device is characterized in that the measurement device measures at least a position component out of the position component, a speed component, and an acceleration component of the elastic vibration, and the compensation device controls the elastic vibration of the object on the basis of position information measured by the measurement device.
According to the fifth aspect of the present invention, a vibration control method using a vibration control apparatus having a first measurement device which measures an elastic vibration of an object to be controlled, a first driving device which applies a force to the object, a first compensation device which determines a force to be generated by the driving device, a second measurement device which measures a position of the object from a reference position, a second driving device which externally applies a force to the object, and a second compensation device which determines a force to be generated by the second driving device is characterized in that the first measurement device measures at least a speed component out of a position component, the speed component, and an acceleration component of the elastic vibration, the first compensation device controls the elastic vibration of the object on the basis of speed information measured by the first measurement device, and the second compensation device controls a rigid-body vibration of the object on the basis of position information measured by the second measurement device.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part hereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.